Structural sandwich plate members

ABSTRACT

A structural sandwich plate member comprises first and second outer plates and a core material of plastics or polymer material. A plurality of lightweight forms are disposed between the outer plates so that the core material forms ribs extending in two substantially orthogonal directions. The lightweight forms may be hollow or solid and manufactured out of foam, plastics or expanded polystyrene. The structural sandwich plate member is preferably formed by injecting the plastics or polymer core material into a closed cavity formed between the outer plates and in which the lightweight forms have been preplaced.

The present invention relates to structural sandwich plate members whichcomprise two outer plates and a core of plastics or polymer materialbonded to the outer plates with sufficient strength to substantiallycontribute to the structural strength of the member.

Structural sandwich plate members are described in U.S. Pat. No.5,778,813 and U.S. Pat. No. 6,050,208, which documents are herebyincorporated by reference, and comprise outer metal, e.g. steel, platesbonded together with an intermediate elastomer core, e.g. of unfoamedpolyurethane. These sandwich plate systems may be used in many forms ofconstruction to replace stiffened steel plates and greatly simplify theresultant structures, improving strength and structural performance(stiffness, damping characteristics) while saving weight. Furtherdevelopments of these structural sandwich plate members are described inInternational Patent Application GB00/04198, also incorporated hereby byreference. As described therein, foam forms may be incorporated in thecore layer to reduce weight and transverse metal sheer plates may beadded to improve stiffness.

According to the teachings of GB00/04198 the foam forms can be eitherhollow or solid. Hollow forms generate a greater weight reduction andare therefore advantageous. The forms described in this document are notconfined to being made of light weight foam material and can also bemake of other materials such as wood or steel boxes.

International Patent Application GB02/01565 is a further development ofthe concept of including hollow forms and describes forms that are easyto manufacture and assemble, in particular hollow elongate forms madefrom snap-together pieces are described.

It is an aim of the present invention to provide structural sandwichplate members including lightweight forms within the core and havingreduced shear deformations under load and improved lateral loaddistribution.

According to the present invention, there is provided: a structuralsandwich plate member comprising: first and second outer plates formedof metal; a core of substantially compact plastics or polymer materialbonded to said outer plates with sufficient strength to transfer shearforces therebetween; and a plurality of relatively lightweight formsdisposed within said core; wherein said lightweight forms are disposedso that there are ribs of said plastics or polymer material extending intwo substantially orthogonal directions in the plane of said platemember, said ribs also extending between said first and second outerplates.

By arranging the lightweight forms such that the plastics or polymermaterial of the core forms ribs extending in two substantiallyorthogonal directions, a better lateral distribution of loads applied tothe plate is obtained, thereby reducing shear deformations of the platemember under load. In use, a load applied locally to the plate memberwill be transferred in two orthogonal directions by the plastics orpolymer material ribs as well as via the outer plates.

The invention may be used with foam and hollow forms as described inInternational Patent Applications GB00/04198 and GB02/01565 as well asany other suitable forms. The lightweight forms serve to reduce the massof the structural sandwich plate member and need not contributesignificantly to its structural strength. The principal requirements onthe lightweight forms are that they are of lower density than theplastics or polymer material forming the core and have sufficientthermal and mechanical properties to maintain the desired shape duringinjection and curing of the plastics or polymer core.

Where the structural sandwich plate member is rectilinear, the ribs mayextend in directions substantially parallel to the edges of the platebut may also extend in directions making an angle to the edges of theplate member.

The materials, dimensions and general properties of the outer plates ofthe structural sandwich plate member of the invention may be chosen asdesired for the particular use to which the structural sandwich platemember is to be put and in general may be as described in U.S. Pat. No.5,778,813 and U.S. Pat. No. 6,050,208. Steel or stainless steel iscommonly used in thicknesses of 0.5 to 20 mm and aluminium may be usedwhere light weight is desirable. Similarly, the plastics or polymer coremay be any suitable material, for example an elastomer such aspolyurethane, as described in U.S. Pat. No. 5,778,813 and U.S. Pat. No.6,050,208.

For some applications, non-metal faceplates, as described in UK patentapplication 0201903.2 entitled “Improved Structural Sandwich PlateMembers” and incorporated herein by reference, may be used. Suchnon-metal faceplates may be made of a reinforced composite or polymermaterial, such as fibre-reinforced polymer material, and havethicknesses in the range of from 1 to 30 mm.

Further, the invention provides a method of manufacturing a structuralsandwich plate member comprising the steps of: providing first andsecond outer plates formed of metal in a spaced-apart relationship witha plurality of lightweight forms located therebetween; injecting uncuredplastics or polymer material to fill the space defined between saidouter plates and said lightweight forms; and allowing said plastics orpolymer material to cure to form a substantially compact material thatbonds said outer plates together with sufficient strength to transfershear forces therebetween; wherein said lightweight forms are disposedso that said plastics or polymer material forms ribs extending in twosubstantially orthogonal directions in the plane of said plate member.

The present invention will be described below with reference toexemplary embodiments and the accompanying schematic drawings, in which:

FIG. 1 is a part-sectional, perspective view of a bridge deck utilisingstructural sandwich plate members according to a first embodiment of thepresent invention;

FIG. 2 is a plan cross-sectional view of a structural sandwich platemember according to a first embodiment of the present invention;

FIG. 3 is a cross-sectional view along the line A-A in FIG. 1;

FIG. 4 is a cross-sectional view along the line B-B in FIG. 1;

FIG. 5 is a view similar to FIG. 1 of a second embodiment of the presentinvention;

FIG. 6 is a cross-sectional view along the line A-A in FIG. 4; and

FIG. 7 is a cross-sectional view along the line B-B in FIG. 4.

In the various drawings, like parts are indicated by like referencenumerals.

FIG. 1 shows a part of a bridge deck 1 in which a structural sandwichplate member according to the present invention may be used. The bridgedeck is in the form of a box girder with deck 2 and soffit 3 formed ofpanels 10 according to the invention of about 5 or 6 m width and about11 or 12 m length. The panels 10 are supported by transverse diaphragms6 at spacings of about 4.5 m. Four panels across the width of the bridgemake a spacing of about 27 m between hangers 4. Faring noses 5 areseparate, non-structural pieces.

FIGS. 2, 3 and 4 are respective plan, longitudinal and lateral sectionalviews of a structural sandwich plate member according to the presentinvention which is suitable for use in the deck of a road bridge. Notethat the longitudinal direction is the direction of primary loadtransfer. The panel 10 may be of the order of 5 to 6 m wide and 10 to 12m long and bear truck loads of total weight 625 kN or greater as part ofa stiffened box girder.

The structural sandwich plate member comprises upper and lower outerplates (faceplates) 11, 12 which may be of steel and have a thickness ofe.g. in the range of from 0.5 to 20 mm. In the present application athickness of 6 mm is suitable. Edge plates are welded between thefaceplates 11, 12 around their outer peripheries to form a closedcavity. In the cavity between the faceplates 11, 12 is a core 14 ofplastics or polymer material, preferably a polyurethane elastomer. Thiscore may have a thickness in the range of from 15 to 200 mm; in thepresent application 160 mm is suitable. The core 14 is bonded to thefaceplates 11, 12 with sufficient strength and has sufficient mechanicalproperties to transfer shear forces expected in use between the twofaceplates. The bond strength between the core 14 and faceplates 11, 12should be greater than 3 MPa, preferably 6 MPa, and the modulus ofelasticity of the core material should be greater than 250 MPa. For lowload applications, such as floor panels, where the typical use andoccupancy loads are of the order of 1.4 kPa to 7.2 kPa, the bondstrength may be lower, e.g. approximately 1 MPa. By virtue of the corelayer, the structural sandwich plate member has a strength and loadbearing capacity of a stiffened steel plate having a substantiallygreater plate thickness and significant additional stiffening.

To reduce the weight of the structural sandwich plate member 10, not allof the volume between the faceplates 11, 12 is occupied by core 13.Instead, an array of lightweight forms 13 is provided, occupying asubstantial part of the internal volume of the plate member. Thelightweight forms 13 do not need to significantly contribute to thestructural strength of the plate and they require only to have thermaland mechanical properties sufficient to withstand the pressure ofinjection of the material to form core 14 and the heat from theexothermic reaction of the core during curing. The lightweight forms 13may be solid or hollow and may for example comprise solid foam blocks,hollow plastic moldings or hollow expanded polypropylene moldings. Theforms are generally rectilinear in shape and laid out in a grid so thatthe core 14 includes a plurality of ribs 15, 16 extending perpendicularand parallel to the long dimension of the forms 13, whilst the formsthemselves extend generally in the short direction of the structuralsandwich plate member 10. In use, the ribs 16 of the core 14 extendingin the long direction of the panel 10, transfer loads to the transversediaphragms 6 whilst the ribs 15 spanning in the short direction of thepanel 10 assist in distributing the load laterally and reduce localshear deformations in the panel. Since the principal load transfer inthe panel is to the transverse diaphragms 6, only a relatively smallnumber of transverse ribs 15 are requited. For example, seven transverseribs 15 in a panel width of about 11 m may suffice. In general, thespacing between transverse ribs may be in the range of from 0.5 to 2 m.

The width of the transverse ribs 15 may be between about 10 and 100 mm;50 mm is suitable in the present application. In cross-section, thetransverse ribs 15 may be rectangular or may be shaped like Ioniccolumns (wider tops and bases) to increase the area of the bond to thefaceplates 11, 12.

The lightweight forms 13 are shown in plan view as having stubs 131 onthree sides thereof. The stubs 131 butt against the adjacent form, or anedge plate of the structural sandwich plate member, to maintain therequired spacing to form the ribs. The stubs 131 do not extend the fullheight of the structural sandwich plate member 10 so that they form onlysmall holes in the ribs of the core rather than interrupting them.Additional stubs 131 may be provided on the top and bottom faces of theforms 13 to space the forms apart from the faceplates 11, 12 creating asubstantially continuous layer of elastomer adjacent each faceplate.Polypropylene spacers may be provided to space the forms 13 away fromthe edges of the structural sandwich plate member.

To manufacture the structural sandwich plate member 10 the edge platesare welded around the periphery of lower faceplate 11 and then forms 13and any spacers placed in the resulting open cavity. At this stage, anyprecast sections of the core may be put in place as well as any shearplates or other fittings that may be desired. Then, the upper faceplate12 is welded to the edge plates to form a closed cavity and the plasticsor polymer material injected to form core 14, including ribs 15, 16. Theinjected material is then allowed to cure and the injection ports usedin the injection step ground off and sealed along with the vent holes.These steps may be performed in situ, or off-site in factory conditionsand the finished panel transported to the installation site.

A structural sandwich plate member according to a second embodiment ofthe present invention is shown in FIGS. 5, 6 and 7 which are viewscorresponding to FIGS. 2, 3 and 4. This plate member may be used as afloor panel, e.g. in a building or floating structure. The structuralsandwich plate member 20 of the second embodiment is similar to that ofthe first but smaller and has only two longitudinal ribs across a widthof about 3 m. In view of the lower loads expected in use, the faceplatesmay have thicknesses of about 3 mm and the core thickness may be 60 mm.In FIGS. 4, 5 and 6 parts of the structural sandwich plate member 20 arelabelled with references corresponding to those of FIGS. 2 to 4 with theaddition of 10. Polypropylene spacers are shown as 27. In thisembodiment, the principal load transfer is across the short dimension ofthe panel, via ribs 26. Transverse ribs 25 assist in load distributionand reduce lateral shear deformations.

In the above embodiments, the transverse ribs are formed when theplastics or polymer material is injected to form the core 13. However,the ribs may also be formed as precast elements which are glued to thefaceplates 11, 12. It will be appreciated that the above description isnot intended to be limiting and that other modifications and variationsfall within the scope of the present invention, which is defined by theappended claims.

1. A structural sandwich plate member comprising: first and second outerplates formed of metal; a core of substantially compact plastics orpolymer material bonded to said outer plates with sufficient strength totransfer shear forces therebetween; and a plurality of relativelylightweight forms disposed within said core; wherein said lightweightforms are disposed so that there are ribs of said plastics or polymermaterial extending in two substantially orthogonal directions in theplane of said plate member, said ribs also extending between said firstand second outer plates.
 2. A structural sandwich plate member accordingto claim 1 and having a rectilinear shape, wherein said twosubstantially orthogonal directions are substantially parallel to theedges of said structural sandwich plate member.
 3. A structural sandwichplate member according to claim 1 and having a substantially rectilinearshape, wherein said substantially orthogonal directions form an acuteangle to the edges of said structural sandwich plate member.
 4. Astructural sandwich plate member according to claim 1, 2 or 3 whereinthe spacing between ribs extending in a first of said two substantiallyorthogonal directions is greater than the spacing between ribs extendingin a second of said two substantially orthogonal directions.
 5. Astructural sandwich plate member according to claim 1, wherein thespacing between ribs extending in said first of said two substantiallyorthogonal directions is in the range of from about 0.5 to about 2 m. 6.A structural sandwich plate member according to claim 1, wherein thethickness of said ribs is in the range of about 10 to about 100 mm.
 7. Astructural sandwich plate member according to claim 1, wherein said ribsextend substantially uninterrupted from one edge of said structuralsandwich plate member to another.
 8. A structural sandwich plate memberaccording to claim 1, wherein said ribs span between said first andsecond outer plates.
 9. A structural sandwich plate member according toclaim 1, wherein said ribs have been formed by injection of saidplastics or polymer material into a space defined between said first andsecond plates.
 10. A method of manufacturing a structural sandwich platemember comprising the steps of: providing first and second outer platesformed of metal in a spaced-apart relationship with a plurality oflightweight forms located therebetween; injecting uncured plastics orpolymer material to fill the space defined between said outer plates andsaid lightweight forms; and allowing said plastics or polymer materialto cure to form a substantially compact material that bonds said outerplates together with sufficient strength to transfer shear forcestherebetween; wherein said lightweight forms are disposed so that saidplastics or polymer material forms ribs extending in two substantiallyorthogonal directions in the plane of said plate member.
 11. (canceled)12. (canceled)